Review on Nanoparticles in Neural Disorders: Alzheimer's, Parkinson's, Stroke, Multiple Sclerosis, Epilepsy, and Huntington's Disease

Particles measuring between 1 to 100 nanometres are defined as nanoparticles [1, 2]. These minuscule particles exhibit diverse physicochemical properties; however, their high surface-area-to-volume ratio renders nanoparticles exceptionally advantageous for numerous biomedical applications [1-4]. These characteristics enable nanoparticles to interact efficiently with biological systems, traverse physiological barriers such as the blood-brain barrier (BBB), and improve the solubility and stability of medicinal compounds [1, 2, 4]. Nanotechnology entails the manipulation of materials at the nanoscale to fabricate novel structures with improved functionality. Nanoparticles can be categorised into several types: organic (e.g., liposomes, micelles, dendrimers, polymeric nanoparticles), inorganic (e.g., metallic, carbon-based), and specifically metallic (e.g., gold, silver, iron) or carbon-based (e.g., carbon nanotubes, nanodiamonds, graphene). Nanoparticles' capacity to transport elevated medication concentrations, support targeted delivery, and permit real-time cellular imaging renders them essential instruments in contemporary medicine, especially for complex ailments like neurological disorders [1,4,5].

1.2 Introduction to Neural Disorders

Neurodegenerative illnesses, including Alzheimer’s disease (AD), Parkinson’s disease (PD), stroke, multiple sclerosis (MS), epilepsy, and Huntington’s disease (HD), constitute a substantial worldwide health challenge owing to their progressive characteristics and intricate aetiology [1,2,5,6]. The global and Indian prevalence of neurological diseases is depicted in Figure 1. Alzheimer's disease is defined by the gradual deterioration of basal forebrain cholinergic neurones, accompanied by memory impairment and cognitive decline, as evidenced by the accumulation of β-amyloid plaques and tau neurofibrillary tangles [1, 3, 5]. Parkinson's disease entails the gradual decline of the central nervous system, caused by a depletion of dopaminergic neurones in the substantia nigra, culminating in motor complications such as dyskinesia and tremors [1, 5, 7]. A stroke occurs when the brain sustains damage from a disrupted blood supply, resulting in neuronal destruction and permanent dysfunction [5]. Multiple sclerosis is a chronic inflammatory disorder of the central nervous system marked by primary demyelination and axonal degeneration. Epilepsy is characterised by irregular electrical activity in brain areas, resulting in recurring and unpredictable seizures [5, 10]. Huntington's disease (HD) is a progressive neurological illness resulting from a CAG repeat expansion in the HTT gene, which causes the degradation of neuronal cells in the brain and affects functional capabilities [1, 5, 11].  A significant obstacle in managing these disorders is the blood-brain barrier (BBB), which inhibits the majority of standard pharmaceuticals from attaining therapeutic levels in the brain [1-3,5-6].

Figure 1: The prevalence of the neural disorders around the globe and in India

2. Aims and Objectives of review

This review aims to critically assess the function of nanoparticles in the diagnosis and treatment of significant neurological disorders—Alzheimer's disease, Parkinson's disease, stroke, multiple sclerosis, epilepsy, and Huntington's disease—by examining their optimal characteristics, mechanisms of action, and clinical applicability. It offers a comparative examination of different nanoparticle kinds and their uses in distinct diseases, emphasising targeted delivery across the blood-brain barrier, prolonged drug release, and therapeutic effectiveness. The study examines recent case studies and clinical trials, identifies current problems in nanoparticle-based neurotherapy, and delineates future opportunities such as smart nanoparticles and personalised nanomedicine for successful neurological treatment.

3. Ideal Properties of Nanoparticles in Neural Disorders: A Comparative Study

For effective detection and treatment of brain diseases, nanoparticles must exhibit a combination of optimal physicochemical and biological characteristics. These encompass elevated biocompatibility, effective blood-brain barrier (BBB) penetration, exact targeted specificity, and regulated release capabilities [3, 5, 12].

3.1 Biocompatibility and Toxicity Considerations

Nanoparticles must exhibit great biocompatibility, allowing interaction with brain tissues without inducing major toxicity, immunological reactions, or persistent inflammation [4-5]. Concerns about toxicity are especially pertinent for metallic and carbon-based nanoparticles, requiring comprehensive evaluations to avert detrimental effects such as oxidative stress, cellular damage, or accumulation in essential organs [1, 4, 13]. The dimensions, morphology, and surface charge of nanoparticles substantially affect their safety profile; for example, smaller nanoparticles may demonstrate heightened toxicity due to enhanced surface reactivity, and rod-shaped nanoparticles can be more cytotoxic than their spherical counterparts. Polymeric nanoparticles, notwithstanding their advantages, may present toxicity hazards stemming from their physicochemical characteristics and possible buildup over time [2].

3.2 Blood-Brain Barrier (BBB) Penetration

Surmounting the blood-brain barrier is the paramount hurdle in neural medication delivery [1-3,5]. Optimal nanoparticles utilise diverse strategies to traverse this barrier, including receptor-mediated transcytosis (e.g., via transferrin receptors), adsorptive-mediated transcytosis (for cationic particles), and carrier-mediated transport (emulating natural substrates such as glucose) [2-3]. Nanoparticles generally must be less than 100 nm in size for effective blood-brain barrier penetration, with certain studies indicating that ultra-small nanoparticles (< 3 nm) may pass through via paracellular diffusion [1]. Surface functionalisation, including PEGylation, can augment stability and diminish non-specific protein adsorption, hence enhancing blood-brain barrier penetration [3, 13, 14].

3.3 Targeting Precision

Accurate targeting of pathological cells or areas reduces off-target effects and enhances therapy effectiveness [3, 5]. This is accomplished by functionalising nanoparticles with specific ligands, antibodies, or peptides that attach to biomarkers that are overexpressed in pathological conditions, as observed in several neurodegenerative diseases [1, 3]. OX26-conjugated selenium nanoparticles specifically target transferrin receptors, which are abundantly expressed on brain capillary endothelial cells, hence enhancing cerebral absorption [14].

3.4 Regulated Release

Controlled release mechanisms guarantee appropriate medication concentrations throughout time, minimising dose frequency and systemic side effects [1-2]. Nanoparticles can be engineered for prolonged release utilising biodegradable polymers or to be stimulus-responsive, discharging their payload in reaction to pH fluctuations, redox potential, or specific enzymes present in the diseased microenvironment [1-3].

4. Comparative Analysis of Nanoparticle Types

5. Nanoparticle Strategies in Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative condition marked by the presence of β-amyloid (Aβ) plaques and tau neurofibrillary tangles. Nanoparticles have exciting opportunities for therapeutic and diagnostic applications in Alzheimer's disease by traversing the blood-brain barrier and targeting specific pathological features. The diverse methodologies pertaining to Alzheimer’s disease are illustrated in Figure 2.

Figure 2.  Nanoparticle-Based Therapeutic and Diagnostic Approaches in Alzheimer’s disease

5.1 Therapeutic Approaches

5.1.1 Amyloid-Targeting Nanoparticles:\

Nanoparticles can impede Aβ aggregation and facilitate the disintegration of pre-existing fibrils. Native poly(D,L-lactide-co-glycolic acid) (PLGA) nanoparticles can inhibit spontaneous Aβ aggregation and dismantle preformed aggregates by engaging with the hydrophobic domains of Aβ. Multifunctional nanoparticles have been engineered to concurrently decrease Aβ synthesis, disrupt fibrils, enhance Aβ metabolic clearance, and modulate oxidative stress. Chiral nanoparticles have demonstrated the ability to expedite the development of neural stem cells (NSCs) into neurones, potentially mitigating Alzheimer's disease pathology.

5.1.2 Tau-Targeting Nanoparticles:

The aggregation of tau protein represents a significant target in Alzheimer's disease. Nanoparticles can transport drugs that inhibit tau hyperphosphorylation and aggregation. A tau-targeted multifunctional nanoinhibitor, consisting of self-assembled polymeric micelles adorned with a tau-binding peptide, effectively obstructs tau aggregation and enhances its proteolytic destruction. Lipid-based nanoparticles containing siRNA have demonstrated the ability to diminish tau protein levels by digesting tau mRNA.

5.1.3 Modulation of Neuroinflammation and Oxidative Stress:

Nanoparticles can transport anti-inflammatory and antioxidant medicines directly to targeted cerebral areas. Polymeric nanoparticles, comprising zwitterionic poly(carboxybetaine)-based and citraconylation-modified PEG–PTMC nanoparticles, have rectified malfunctioning microglia, diminished pro-inflammatory cytokines, and enhanced mitochondrial activity. Selenium nanoparticles, due to their potent antioxidant properties, have demonstrated potential in mitigating Alzheimer's disease by reducing oxidative stress in the brain. Gold nanoparticles (AuNPs) demonstrate neuroprotective properties by neutralising reactive oxygen species (ROS) and regulating inflammatory responses.

5.1.4 Stem Cell Integration:

Nanotechnology augments stem cell therapy for Alzheimer's disease by optimising targeted distribution and enhancing regenerative results. Human Wharton’s jelly-derived mesenchymal stem cells, labelled with superparamagnetic iron oxide nanoparticles (SPIONs), can be magnetically directed to the hippocampus, enhancing cell viability and functionality. Human brain stem cells modified with gold nanoparticles exhibit a protective effect against Aβ-induced cellular damage and mitochondrial dysfunction.

5.1.5 Gene Therapy:

Nanoparticles facilitate the delivery of genetic material for therapeutic gene modification. Peptide-delivered CRISPR-Cas9 nanocomplexes have been employed for in vivo gene editing, specifically targeting the Bace1 gene to diminish Aβ peptide formation, resulting in cognitive enhancements in murine models. Non-viral gene delivery systems utilising mesoporous silica nanoparticles or heparinised cationic solid lipid nanoparticles have been engineered to generate specific cell lines from induced pluripotent stem cells (iPSCs) for neuronal development.

5.2 Diagnostic Methodologies

Nanoparticles function as diagnostic instruments by augmenting imaging capabilities. SPIONs, owing to their magnetic characteristics, facilitate the real-time monitoring of transplanted stem cells in vivo by MRI. Gold nanoparticles are utilised for imaging owing to their optical characteristics and can be functionalised with antibodies to identify Aβ aggregates, hence evaluating disease severity. Theranostic nanoparticles integrate diagnostic and therapeutic capabilities, facilitating concurrent imaging and treatment of Alzheimer's disease pathology.

6. Nanoparticle Strategies in Parkinson's Disease

Parkinson's disease (PD) is defined by the loss of dopaminergic neurones in the substantia nigra, resulting in both motor and non-motor symptoms. Nanoparticles present intriguing approaches for drug delivery, neuroprotection, and disease modification in Parkinson's disease.

6.1 Pharmaceutical Administration

Nanoparticles markedly enhance the transport of therapeutic substances across the blood-brain barrier (BBB), a critical obstacle for Parkinson's disease medications.

6.1.1 Dopamine Substitution Therapies:

Poly(D,L-lactic-co-glycolic acid) (PLGA) nanoparticles, frequently coated with albumin, can encapsulate dopamine and levodopa, facilitating prolonged release and improved cerebral delivery. These formulations have demonstrated greater durability in motor enhancements in mouse models relative to traditional levodopa therapy, hence decreasing the dosage frequency. Intranasal delivery of nanoparticles co-modified with borneol and lactoferrin has demonstrated enhanced therapeutic efficacy by increasing blood-brain barrier permeability and specifically targeting the striatum.

6.1.2 Targeted Delivery:

Magnetic nanoparticles can guide stem cells to certain brain locations, which is essential for the treatment of conditions such as Parkinson's disease. Magnetic nanoparticle-enhanced human adipose stem cells augment stem cell-based therapy for Parkinson's disease.

6.2 Neuroprotection and Disease Modification

Nanoparticles provide neuroprotection by influencing critical pathogenic mechanisms in Parkinson's disease, such as oxidative stress, neuroinflammation, and protein aggregation.

6.2.1 Antioxidant and Anti-inflammatory Effects:

Injectable bioactive hydrogels incorporating tannic acid and gold nano-crosslinkers have demonstrated the ability to promote the proliferation and differentiation of brain stem cells, alongside demonstrating anti-inflammatory and antioxidative properties. Gold nanoparticles (AuNPs) exhibit neuroprotective properties in Parkinson's disease by reducing inflammation and oxidative stress in both in vitro and in vivo models. Curcumin-encapsulated nanodecoys can reinstate dopamine concentrations, enhance blood-brain barrier permeability, diminish alpha-synuclein clumps, and modulate mitochondrial activity.

6.2.2 Stem Cell Enhancement:

Engineered mesenchymal stem cells utilising dextran-coated iron oxide nanoparticles have enhanced differentiation into dopaminergic neurones and increased neuroprotection. Neural stem cells treated with biocompatible and traceable polymeric nanoparticles expressing microRNA-124 have facilitated neuronal development and augmented natural brain healing processes.

6.2.3 Alpha-Synuclein Modulation:

Gold-doped TiO nanotubes may identify alpha-synuclein, while Nerve Growth Factor-conjugated Au particles have inhibited alpha-synuclein aggregation.

6.3 Novel Neuromodulatory Strategies

6.3.1 Upconversion Nanoparticles:

These nanoparticles convert near-infrared light, which penetrates deeply into tissues, into visible light to trigger genetically modified opsin-expressing cells, facilitating non-invasive optogenetic stimulation.

6.3.2 Magnetothermal Nanoparticles:

These convert external magnetic fields into thermal energy, influencing genetically engineered cells that exhibit heat-sensitive ion channels, hence facilitating targeted neuromodulation.

6.3.3 Magnetoelectric Nanoparticles:

These entities transmute magnetic energy into electric fields, enabling the modulation of local neural activity without genetic alteration, and certain types can be delivered peripherally to traverse the blood-brain barrier.

6.3.4 Ultrasound-Responsive Nanoparticles:

These nanoparticles can be stimulated by focused ultrasound to discharge their therapeutic payload or produce electric currents, facilitating precise, localised medication administration or neuronal activation.

7. Nanoparticle Strategies in Stroke

Stroke, predominantly ischaemic, occurs due to the cessation of cerebral blood flow, resulting in neuronal damage and mortality. Nanoparticles are under investigation for targeted thrombolysis, neuroprotection, and enhanced imaging in stroke treatment.

7.1 Focused Thrombolysis

Nanoparticles can improve the administration and effectiveness of thrombolytic drugs. They can adhere to thrombi, offering both therapeutic and imaging capabilities to assess clot breakdown. The materials do not specify nanoparticle-based thrombolytic medicines but emphasise the possibility for targeted delivery systems for therapeutic drugs in the brain.

7.2 Neuroprotection

Nanoparticles provide neuroprotection by addressing inflammation, oxidative stress, and enhancing neuronal survival following ischaemic events.

7.2.1 Selenium Nanoparticles:

OX26-Polyethylene GlycolOxidised selenium nanoparticles (OX26-PEG-Se NPs) have exhibited considerable neuroprotective effects in mouse models of ischaemic stroke. These nanoparticles mitigate brain oedema, diminish infarction volumes, and safeguard axons in the hippocampal region, resulting in enhanced locomotor function. OX26-PEG-Se NPs do this by mitigating excessive inflammation and oxidative metabolism, altering critical signalling pathways like mTOR, FoxO1, Wnt/β-Catenin, and Jak2/Stat3, while fostering protective autophagy and preventing apoptosis. They additionally bolster endogenous antioxidant defences and preserve the integrity of the extracellular matrix.

7.2.2 Gold Nanoparticles (AuNPs):

Gold nanoparticles (AuNPs) exhibit neuroprotective properties in ischaemic stroke models via mitigating oxidative stress and inflammation.

7.3 Imaging Techniques

Nanoparticles facilitate stroke diagnosis and monitoring by improving imaging techniques. Magnetic nanoparticles can be utilised to monitor cellular migration to lesion locations by magnetic resonance imaging (MRI).

8. Nanoparticle Strategies in Multiple Sclerosis

Multiple sclerosis (MS) is an autoimmune disorder of the central nervous system marked by inflammation, demyelination, and neurodegeneration. Nanoparticle-based therapies seek to enhance drug distribution, facilitate immunomodulation, and encourage remyelination, as illustrated in Figure 3.

Figure 3.  Nanoparticle-Based Therapeutic and Diagnostic Approaches in Multiple Sclerosis

8.1 Targeted Delivery Mechanisms

The blood-brain barrier is a considerable obstacle for drug delivery in multiple sclerosis, and nanoparticles provide a potential solution.

8.1.1 Liposomes:

Artificial vesicles, such as liposomes, can encapsulate therapeutic substances and traverse the blood-brain barrier to deliver medications to central nervous system lesions. Liposomes containing antigenic myelin peptides can elicit immunological tolerance, hence diminishing inflammation. PEGylated liposomes containing steroids have demonstrated enhanced clinical outcomes in experimental autoimmune encephalomyelitis (EAE), a model for multiple sclerosis (MS).

8.1.2 Polymeric Nanoparticles:

These can be designed to improve medication solubility, bioavailability, and regulated release. Biodegradable poly(lactic-co-glycolic acid) (PLGA) nanoparticles containing myelin antigens can elicit strong tolerance and prolonged disease prevention in multiple sclerosis models. Chitosan nanoparticles encapsulating siRNA can promote neuroprotection and remyelination by downregulating proteins that inhibit myelination.

8.2 Immunomodulation

Nanoparticles can influence immunological responses to restore immune tolerance and diminish the autoimmune assault on myelin.

8.2.1 Antigen-Specific Immunotherapy:

PLGA nanoparticles can integrate the delivery of antigens with immunomodulatory agents such as interleukin-10 (IL-10) or rapamycin to elicit antigen-specific regulatory T cells, therefore markedly diminishing disease severity in multiple sclerosis models.

8.2.2 Extracellular Vesicles (EVs):

EVs emitted from brain cells, such as microglia, can function as drug carriers and possess therapeutic promise in multiple sclerosis (MS). Engineered electric vehicles can transport various functional chemicals, including anti-inflammatory medicines, for the treatment of neuroinflammatory illnesses. MSC-derived exosomes containing TGF-β, PD-L1, and Gal-1 can suppress the activation of autoreactive lymphocytes.

8.3 Remyelination

Nanoparticles enhance remyelination by stimulating the recruitment and differentiation of oligodendrocyte progenitor cells (OPCs).

8.3.1 Targeted Growth Factors:

PLGA nanoparticles modified with antibodies can specifically target oligodendrocyte precursor cells (OPCs) and distribute leukaemia inhibitory factor (LIF) to promote remyelination.

8.3.2 Selenium Nanoparticles:

Oral administration of nanolipidic carriers containing vitamins and selenium has demonstrated enhanced clinical outcomes and remyelination in models of demyelination.

8.4 Gold Nanocrystals:

A suspension of gold nanocrystals (CNM-Au8) markedly ameliorated deficiencies in metabolites associated with cerebral energy metabolism and led to functional enhancements in multiple sclerosis patients during phase two clinical studies.

9. Nanoparticle Strategies in Epilepsy

Epilepsy is a neurological disorder marked by irregular electrical activity and frequent seizures. Nanoparticles provide alternatives for targeted drug administration, enhanced seizure management, and manipulation of the blood-brain barrier (BBB), overcoming the limitations of traditional anti-seizure drugs (ASMs) like low brain bioavailability and drug resistance.

9.1 Focused Pharmacological Administration

Nanoparticles augment the bioavailability of antiseizure medications (ASMs) within the central nervous system (CNS) by facilitating their traversal across the blood-brain barrier (BBB) more efficiently.

9.1.1 Polymeric Nanoparticles (PNP):

PNPs can encapsulate antiepileptic medications such as oxcarbazepine (OXC) and carbamazepine (CBZ), resulting in enhanced efficacy and decreased administration frequency in animal models. PLGA nanoparticles have been utilised to transport substances including epigallocatechin-3-gallate (EGCG) and thyrotropin-releasing hormone (TRH) analogues, exhibiting neuroprotective and anticonvulsant properties. PNPs safeguard pharmaceuticals from enzymatic breakdown and immunological response while regulating release kinetics.

9.1.2 Lipid Nanoparticles (LNP):

Solid lipid nanoparticles (SLN) and nanostructured lipid carriers (NLC) exhibit remarkable versatility owing to their little toxicity and substantial drug loading capability. They can enhance medication absorption and precisely target certain parts of the brain. For example, alprazolam-loaded solid lipid nanoparticles exhibited enhanced cerebral concentration and targeting efficacy when delivered via the intranasal route. Curcumin-loaded solid lipid nanoparticles have exhibited neuroprotective efficacy against oxidative damage in vitro. NLCs containing valproic acid exhibit a neuroprotective effect comparable to traditional treatment but at reduced levels through intranasal delivery.

9.2 Management of Seizures

Nanoparticles enhance seizure management by elevating medication concentrations at epileptic foci, thereby diminishing seizure frequency and intensity. The encapsulation of carbamazepine (CBZ) in polymeric nanoparticles (PNPs) rendered it 30 times more efficacious against seizures compared to free CBZ and facilitated the circumvention of P-glycoprotein-mediated drug resistance, a prevalent factor in treatment failure.

9.3 BBB Modulation

Nanoparticles can alter blood-brain barrier permeability, facilitating enhanced medication penetration. Certain nanoparticles can penetrate epithelial cells constituting the blood-brain barrier or aggregate on its luminal surface, hence enhancing drug ingress into the brain. The structural resemblance of lipid nanoparticles to endothelial cell lipids facilitates their transit through the transcellular pathway.

10. Nanoparticle Strategies in Huntington's Disease

Huntington’s disease (HD) is a hereditary neurodegenerative disorder marked by the gradual deterioration of neuronal cells in the brain, predominantly caused by a CAG repeat expansion in the HTT gene, resulting in the aggregation of mutant huntingtin (mHTT) protein. Nanoparticles present opportunities for gene therapy, neuroprotection, and the administration of disease-modifying drugs in Huntington's disease.

10.1 Gene Therapy

Nanoparticles function as vehicles for nucleic acid-based therapies designed to diminish the expression of the mutant huntingtin gene. The documents do not specify particular gene therapy methods for HD utilising nanoparticles; however, they highlight the capability of nanoparticles to deliver therapeutic genes or gene-editing elements, such as CRISPR/Cas9, directly to impacted neurones, thereby avoiding systemic exposure and minimising off-target effects. The efficacy of nanoparticle-mediated non-viral gene delivery techniques is a primary emphasis.

10.2 Neuroprotection

Nanoparticles are employed to transport neuroprotective medicines to alleviate the consequences of mHTT aggregation and related cellular injury.

10.2.1 Targeting Protein Aggregation:

A nanoparticle formulation of trehalose has been engineered with a zwitterionic surface charge and multivalency, demonstrating superior efficacy compared to molecular trehalose in preventing protein fibrillation and obstructing the aggregation of polyglutamine-containing mutant huntingtin protein in neuronal cells.

10.2.2 Promotion of Cellular Autophagy:

Iron oxide/zinc oxide nanoparticles coated with hemin/amine/arginine/trehalose have been shown to stimulate cellular autophagy and enhance cell survival, essential for the clearance of aggregated proteins in Huntington's disease.

10.2.3 Augmenting Neural Stem Cell Function:

Ferritin nanoparticles have been designed to improve the self-renewal and differentiation of neural stem cells and neural progenitor cells, potentially aiding brain health and regeneration in Huntington's disease.

Magnetic nanoparticles have been studied to control the size of human embryoid bodies, so improving the neural development efficiency of human embryonic stem cells.

10.3 Administration of Disease-Modifying Agents

Nanoparticles facilitate the precise administration of drugs intended to alter the progression of the disease rather than merely alleviate symptoms.

10.3.1 Magnetic Guidance:

Superparamagnetic iron oxide nanoparticles labelled mesenchymal stem cells have demonstrated a reduction in cell tracking and cerebral damage in a rat model of Huntington’s disease, while human embryonic stem cells labelled with these nanoparticles mitigated motor impairment. Magnetic nanoparticles can guide stem cells to certain brain areas for therapeutic purposes.

10.3.2 Enhancing Neuronal Differentiation:

The efficacy of nerve growth factor and gold-chitosan nanoparticles has been evaluated for their ability to induce the differentiation of human adipose-derived stem cells into Schwann-like cells, which are crucial for nerve health.

11. Case Studies and Clinical Trials on Nanoparticles Utilised for the Treatment of Neurological Disorders

Although several nanoparticle-based strategies for neurological diseases remain in preclinical phases, several attractive candidates have progressed to clinical trials, providing insights into their translational viability.

11.1 Gold Nanocrystals (CNM-Au8) for Mass Spectrometry and Photodetection

An exemplary case is the phase two clinical trials of CNM-Au8, an orally administered suspension of gold nanocrystals, for individuals with multiple sclerosis (MS) and Parkinson’s disease (PD).

Study Design: Two phase II clinical trials, REPAIR-MS and REPAIR-PD, were executed at UT Southwestern Medical Centre. Participants underwent an initial brain magnetic resonance spectroscopy scan to ascertain their baseline NAD+/NADH ratio and other energy metabolites. Subsequently, they administered a daily dosage of CNM-Au8 for 12 weeks, after which a second MR spectroscopy and functional outcome evaluations were conducted.

The study revealed that CNM-Au8 substantially ameliorated deficiencies in metabolites associated with cerebral energy metabolism, especially elevating the NAD+/NADH ratios by an average of 10.4% relative to baseline measurements. Other energy molecules, such as ATP, returned to baseline levels by the conclusion of the treatment. Patients with Parkinson's disease reported enhanced motor sensations in daily activities. Importantly, none of the patients saw significant adverse effects associated with CNM-Au8.

Translational Significance: These findings are cautiously encouraging and indicate that this method may prevent or potentially reverse certain neurological impairments. The research underscores the capacity of gold nanocrystals to beneficially modify the energy equilibrium of brain cells, a process evidenced in prior cellular and animal studies.

11.2 Additional Clinical Research and Trials

11.2.1 Parkinson’s Disease Drug Delivery:

Although human clinical trials utilising PLGA nanoparticles for Parkinson’s disease drug delivery have not commenced, preclinical studies in mouse models have demonstrated enhancements in motor function persisting for a minimum of 7 days, indicating a more sustained advantage compared to existing levodopa treatment. Researchers are currently organising human trials informed by these findings.

11.2.2 Blood-Brain Barrier Opening:

Low-intensity focused ultrasound (LIFU) in conjunction with microbubbles has been employed in clinical trials for the purpose of opening the blood-brain barrier in neuro-oncology and Alzheimer's disease. A proof-of-concept trial including seven patients with Parkinson's disease dementia successfully demonstrated transitory opening of the striatal blood-brain barrier, which was well-tolerated. A separate study examined LIFU-induced BBB permeability for glucocerebrosidase administration in Parkinson's disease patients with GBA1 mutations, demonstrating enhanced motor scores.

11.2.3 Gene Therapy:

Initial trials of viral vector-based gene therapy raised safety concerns; nevertheless, recent developments have resulted in FDA-approved gene editing medicines for illnesses such as spinal muscular atrophy. Clinical trials for Parkinson's disease have concentrated on enhancing central nervous system dopamine by altering biosynthetic routes or expressing enzymes such as glutamic acid decarboxylase (GAD). These trials, which necessitate neurosurgical injection, have demonstrated favourable safety profiles and promising enhancements in motor symptoms. CRISPR-based gene editing is advancing, with prospects for non-viral delivery using nanoparticles, however it has not yet entered clinical trials for central nervous system illnesses.

These case studies and trials illustrate the continuous endeavours and initial achievements in converting nanoparticle technology from preclinical research to human applications in neurological illnesses.

12. Nanoparticle-Driven Approaches for Targeted Treatment in Neurological Disorders: Mechanisms, Applications, and Clinical Implications

The application of nanoparticles in the treatment of neurological illnesses has attracted considerable attention owing to their ability to traverse the blood-brain barrier (BBB), facilitate targeted medication delivery, and offer controlled release mechanisms. This overview delineates the therapeutic potential of diverse nanoparticle systems for significant neurological diseases as presented in Table 1.

Lipid-based nanoparticles, such as liposomes, have demonstrated potential in Alzheimer's disease by improving the encapsulation and distribution of neuroprotective medicines, hence boosting cognitive performance [1]. PLGA-based polymeric nanoparticles facilitate prolonged dopamine administration in Parkinson's disease, providing neuroprotective advantages [2]. Gold nanoparticles demonstrate anti-inflammatory and antioxidant qualities advantageous in Multiple Sclerosis, mitigating demyelination [3], whereas iron oxide nanoparticles facilitate targeted imaging and treatment in glioblastoma owing to their magnetic characteristics [4].

Carbon-based nanoparticles, such as graphene oxide, have reactive oxygen species (ROS) scavenging capabilities, enhancing motor neurone viability in ALS [5]. Silica nanoparticles improve drug delivery in Alzheimer's disease by controlled release and targeted transport across the blood-brain barrier. Cerium oxide nanoparticles mitigate oxidative stress in Parkinson's disease, hence promoting the health of dopaminergic neurones [7].

In brain imaging, quantum dots function as fluorescent probes to define tumour boundaries in glioblastoma [8]. Dendrimers, due to their modifiable surface, facilitate gene and medication delivery in Huntington's disease, enhancing siRNA administration [9]. PEGylated nanoparticles, which prolong circulation, enhance thrombolytic delivery in stroke treatment [10], whereas chitosan nanoparticles provide regulated antiepileptic medication delivery in epilepsy [11].

Albumin nanoparticles augment levodopa bioavailability in Parkinson’s disease [12], while solid lipid nanoparticles facilitate the delivery of polyphenols such as curcumin and resveratrol in Alzheimer’s disease [13].

These nanocarriers signify a breakthrough in neurotherapeutics, offering increased efficacy, diminished adverse effects, and better patient outcomes for many neurological illnesses.

Table-1: Nanoparticle-Based Strategies for Targeted Therapy in Neurological Disorders: Mechanisms, Applications, and Clinical Impact